This invention relates to an implantable joint head which is used to replace the head of the femur of the human body which has been damaged by fracture or malum coaxe deformans.
When an implantable joint head of this type is put on the market, it is necessary to provide its historical data, such as, marking it with a manufacture number. This marking will be described with reference to FIG. 4. In a conventional marking method, after an implantable joint head 1 of ceramic is sintered, numerical data or the like is engraved with an edged tool on the end face 2, in which a recess is opened, or on the outer spherical surface 3. Thereafter, a metal stem (not shown) is fixedly inserted into the recess 4 to complete the manufacture of the implantable joint head.
In another method, after an implantable joint head is sintered, a manufacture number or the like is marked on it with a laser or ultrasonic marking machine, and then a metal stem is fixed into the recess.
As described above, in the conventional marking method, the surface of the implantable joint head is scratched by the marking method. In other words, a number of defects, namely, scratches, are formed in the surface. In this connection, a static load strength test revealed that an implantable joint head with an engraved end face has about a 25% lower mechanical strength than one which is not engraved.
Furthermore, it is rather difficult to put a marking on the narrow surface of the end face according to the conventional marking method.